Monitoring Water in Automotive Lubricants with Fourier Transform Infrared Spectroscopy

The presence of water in lubricants can cause a variety of quality and performance problems (1). Depending on the lubricant type and application, excessive water can cause additive fall out or hydrolysis, corrosion and pitting of metal surfaces during use, interference with surface active additives such as friction modifiers, foaming of the lubricant and filter plugging. Quality checks for water are commonly done using techniques such as visual inspection, crackle test, measurement of dielectric breakdown voltage (2) or Karl Fischer titration (3). Of these, only Karl Fischer titration is truly quantitative. Quantitation of water can be complicated by the presence of hydrophilic additives, which attract and bind water. Fourier Transform Infrared Spectroscopy (FTIR) can be used as a screening test because the presence of water will cause a broad absorbance peak to appear at about 3400 cm^-1 due to the OH stretch.

The use of FTIR is examined for the accurate determination of water in new, formulated oils. It has been compared to Karl Fischer titration for ease of use and for approximate detection limits in four different types of automotive fluids: gear oil, heavy duty engine oil, passenger car motor oil and tractor hydraulic oil. The viability of the routine use of FTIR was also compared to the other more common, non-quantitative methods described above.